Determine whether mitochondria from ischemic heart muscle are functionally impaired in situ. Mitochondria will be isolated from ischemic rat heart muscle at various times after partial restriction of flow through the coronary arteries. Normal mitochondria will be studied under conditions which simulate different aspects of the abnormal environment of the ischemic cell. Attempts will be made to learn whether reversible or irreversible impairment of mitochondrial function correlates chronologically with irreversible damage to the ischemic heart.